Once again, I appreciate all the replies to the rokkyo question.
It seems I led a digression to the yonkyo question, and I'd like to clarify it. As I discussed the pressure point pain that was caused, I didn't mean to imply that pain was the "end", rather it's the "means" to the technique, that is to effect the technique with an "off-balancing" of the mind caused by the momentary pain.
One thing I must disagree with, though, are the mentions in this thread that pressure points are incidental or not necessary in aikido. When you read accounts of O-Sensei's techniques by people who served as his ukes, they say he was using pressure points all the time. Also, take a look at the video of O-Sensei grasping the hand of a young Terry Dobson and leading him all over the place, all bent over - I don't know for sure what's going on, but it looks to me like pressure points, not a joint lock.
Please don't take this for any more or any less than this - I'm not a kyusho jitsu guy or anything like that. But, techniques like ikkyo, nikkyo, sankyo, yonkyo, shihonage - they've all got pressure point applications in them, and to me they're really nothing but a different type of atemi that quickly unfocuses uke's mind in preparation for a pin or throw.